1. Field of the Invention
The present invention relates to a method and apparatus for controlling the drive frequency of an LED and, more particularly, for controlling the drive frequency control of an LED for a radio receiver.
2. Description of the Related Art
A radio receiver, for example, a selective calling receiver including a paging receiver, indicates an incoming call by activating a light source (LED). The drive frequency of the LED is determined so as to make the luminance of the LED be the largest. Therefore, the amount of current required becomes large and a battery life of the receiver is reduced.
Recently, an air-zinc battery having a large internal resistance has been used as a DC power source for the receiver. The air-zinc battery has a characteristic that the smaller the residual capacity, the larger the internal resistance, and an additional characteristic that the lower the ambient temperature and ambient moisture, the larger the internal resistance. Hence, it is possible for the cell voltage to fall by a large current, e.g., ten mA or more, such that the voltage of an alkaline cell or a manganese cell decreases to a voltage which is insufficient to operate the receiver.